Selectable drivetrain control for a vehicle

ABSTRACT

A selectable drivetrain control for a vehicle includes a controller configured to receive input signals and issue predetermined output command signals corresponding to the status of the input signals. A first sensor is configured to provide an input signal to the controller relating to the actuation status of a brake pedal. A second sensor is configured to provide an input signal to the controller relating to the actuation status of an accelerator pedal. A stability control selector is configured to provide an input signal to the controller relating to the engagement status of a stability control system of the vehicle. A drivetrain is configured to receive output command signals from the controller. The controller issues output command signals to the drivetrain to control the operational characteristics of the drivetrain, responsive to the engagement status of the stability control system while the brake and accelerator pedals are simultaneously actuated.

This application is a divisional of co-pending U.S. patent applicationSer. No. 11/686,062, filed Mar. 14, 2007, the entire contents of whichare hereby incorporated herein by reference thereto.

FIELD

The present invention relates generally to a selectable drivetraincontrol for a vehicle, in particular to a control to selectably set atransmission gear position, limit the displacement of a throttle andlimit ignition timing while the vehicle's brake and accelerator pedalsare simultaneously actuated.

BACKGROUND

A motor vehicle driver typically controls the speed of a conventionalvehicle using foot pedals, which in a vehicle with an automatictransmission are the accelerator pedal and the brake pedal. Drivers willnormally use the same foot to control both the accelerator pedal and thebrake pedal. However, some drivers of automatic transmission vehiclesuse two feet, one to actuate the accelerator pedal and the other toactuate the brake pedal. This can result in simultaneous activation ofboth the vehicle brake and throttle. In certain situations a stallcondition may occur due to simultaneous activation of both the brake andthe throttle, subjecting the vehicle's drivetrain to significant stress.

Others have attempted to limit drivetrain stress due to simultaneousactuation of the vehicle's brake and accelerator pedals by reducing orlimiting the throttle setting under such conditions, thereby limitingthe amount of torque generated by the vehicle's engine and delivered toa transmission system. An example may be found in U.S. Pat. No.6,125,315, issued to Kon, the contents of which are hereby incorporatedherein by reference. The system disclosed by Kon limits the degree ofopening of the throttle when a stall condition is detected, therebyreducing stress imposed on the vehicle's drivetrain. However, suchsystems do not address the unique stresses imposed upon a four-wheeldrivetrain when a vehicle is operated such that the brake andaccelerator pedals are actuated under road conditions wherein some, butnot all, of the wheels lose traction.

For example, many vehicles are now equipped with an “on-demand”four-wheel drive transmission system wherein a varying amount of torqueis provided to each axle in order to maintain traction under varyingroad conditions. One of the most severe of these road conditions occurswhen the wheels of one axle of the vehicle lose traction due to, forexample, ice or snow while the wheels of the other axle retain traction.When launching the vehicle from a stalled state under these conditions alarge amount of torque is transferred to the axle having traction due tothe lack of traction in the other axle, thereby imposing significantstress upon the drivetrain. However, if a vehicle under the sameconditions is equipped with a vehicle stability control system theamount of torque transferred to the axle having traction may be reducedbecause the vehicle stability system limits and compensates for a lossof traction in the other axle by reducing engine power and applyingbrake intervention to reduce wheel slip on low traction surfaces. Thisreduction of wheel slip reduces the amount of torque transferred to theaxle having traction, thereby reducing stress on the drivetrain.

It would be desirable to utilize a vehicle's traction control system inconjunction with a throttle limiting system in order to tailor theoperating performance of the vehicle under stall launch conditionswherein the brake and throttle are activated simultaneously. Such asystem would be particularly useful for increasing the operatingperformance of an on-demand four-wheel drive transmission under varyingroad conditions while still protecting the drivetrain from damage.

SUMMARY

The present invention utilizes the engagement status of a vehiclestability/traction control system to establish the operationalparameters of the vehicle's drivetrain when the brake and acceleratorpedals are simultaneously actuated. In a first “performance”configuration, when the vehicle stability/traction control is engaged bythe driver and the brake and accelerator are simultaneously actuated,the vehicle's transmission is automatically placed into first gear andthe vehicle's throttle is automatically set to a predetermined reducedsetting. Conversely, in a second “preservation” configuration, when thevehicle stability/traction control is disengaged by the driver and thebrake and accelerator pedals are simultaneously actuated, thetransmission is placed into second gear while the throttle is set to apredetermined reduced setting that is lower than that of the“performance” configuration.

One aspect of the present invention is a selectable drivetrain controlfor a vehicle. The drivetrain control includes a controller configuredto receive input signals and issue predetermined output command signalscorresponding to the status of the input signals. A first sensor isconfigured to provide an input signal to the controller relating to theactuation status of a brake pedal. A second sensor is configured toprovide an input signal to the controller relating to the actuationstatus of an accelerator pedal. A stability control selector isconfigured to provide an input signal to the controller relating to theengagement status of a stability control system of the vehicle. Adrivetrain is configured to receive output command signals from thecontroller. The controller issues output command signals to thedrivetrain to control the operational characteristics of the drivetrain,responsive to the engagement status of the stability control systemwhile the brake and accelerator pedals are simultaneously actuated.

Another aspect of the present invention is a method for controlling theoperational characteristics of a drivetrain of a vehicle. The methodincludes the steps of monitoring the actuation status of a brake pedal,an accelerator pedal and a stability control system of the vehicle.While both the brake pedal and accelerator pedal are simultaneouslyactuated and the stability control system is not engaged, a throttle ofan engine of the drivetrain is set to a first predetermined position. Anengine ignition timing advance is set to a position corresponding to thefirst throttle position. A first gear setting of a transmission of thedrivetrain is also selected. While both the brake pedal and acceleratorpedal are simultaneously actuated and the stability control system isengaged, the throttle is set to a second predetermined position.Furthermore, the ignition timing advance is set to a positioncorresponding to the second throttle position. Lastly, a secondtransmission gear setting is selected.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the inventive embodiments will become apparent tothose skilled in the art to which the embodiments relate from readingthe specification and claims with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic block diagram showing the general arrangement of arelevant portion of a vehicle drivetrain control system according to anembodiment of the present invention;

FIG. 2 is a flow diagram showing operational steps associated with thesystem of FIG. 1;

FIG. 3A is a graph of throttle response versus depression of anaccelerator pedal with respect to time for a first condition of thesystem of FIG. 1;

FIG. 3B is a graph of engine ignition timing advance with respect totime for a first condition of the system of FIG. 1;

FIG. 3C is a graph of brake pedal actuation state with respect to timefor a first condition of the system of FIG. 1;

FIG. 3D is a graph of transmission gear setting with respect to time fora first condition of the system of FIG. 1;

FIG. 4A is a graph of throttle response versus depression of anaccelerator pedal with respect to time for a second condition of thesystem of FIG. 1;

FIG. 4B is a graph of engine ignition timing advance with respect totime for a second condition of the system of FIG. 1;

FIG. 4C is a graph of brake pedal actuation state with respect to timefor a second condition of the system of FIG. 1; and

FIG. 4D is a graph of transmission gear setting with respect to time fora second condition of the system of FIG. 1.

DETAILED DESCRIPTION

A schematic block diagram showing the general arrangement of a relevantportion of a drivetrain control system 10 for a vehicle according to anembodiment of the present invention is shown in FIG. 1. System 10comprises a controller 12 configured to control the operation of adrivetrain 14 coupled thereto. Drivetrain 14 includes in pertinent parta transmission gear selector 16 that is coupled to an automatictransmission 18. Drivetrain 14 further includes a throttle positionactuator 20 and an ignition timing control 22, each coupled to an engine24.

Controller 12 receives status signals from any or all of a brake pedalstate sensor 26, an accelerator pedal state sensor 28, and a stabilitycontrol selector 30, and controls the operation of system 10 in apredetermined manner. Example control tasks for controller 12 mayinclude, without limitation, providing predetermined output commandsignals to any or all of transmission gear selector 16, throttleposition actuator 20 and ignition timing control 22, the command signalscorresponding to the condition of the status signals. Controller 12 mayalso detect fault conditions with the components of system 10 and/orinterconnections thereof. Non-limiting example fault conditions mayinclude internal faults within controller 12, open or shorted electricalconnections, low input power supply voltage to system 10, andpredetermined fault conditions present in any or all of transmissiongear selector 16, throttle position actuator 20 ignition timing control22, brake pedal state sensor 26, accelerator pedal state sensor 28 andstability control selector 30. Controller 12 may be configured usingconventional analog or digital electronic circuitry or a combinationthereof, and may utilize conventional memory devices such as magnetic,electronic and optical memory storage devices containing a predeterminedset of instructions, such as a computer program.

Transmission gear selector 16 may be any type of device suitable forreceiving an electrical gear selection command signal from controller 12and selecting a corresponding gear setting of automatic transmission 18.Example devices include, without limitation, actuators, clutches,solenoids, relays and electro-hydraulic cylinders. Transmission gearselectors are well-known in the art and thus will not be detailedfurther herein.

Transmission 18 may be any conventional type of automatic transmissionconfigured to transmit power from engine 24 to a set of drive wheels(not shown) including, without limitation, a front-wheel drivetransmission, rear-wheel drive transmission, a selectable four-wheeldrive transmission, an all-wheel drive transmission and an on-demandfour-wheel drive transmission. Such transmissions are well-known in theart and thus will not be detailed further herein.

Throttle position actuator 20 may be any conventional type of devicesuitable for receiving an electrical throttle command signal fromcontroller 12 and setting an air/fuel mixture of a fuel supply forengine 24 to a predetermined flow quantity and mixture ratiocorresponding in a predetermined manner to the electrical throttlecommand, resulting in a predetermined engine speed. Example throttleposition controls include, without limitation, electro-mechanicalactuators, electro-hydraulic cylinders, and relays. Throttle positionactuators are well-known in the art and thus will not be detailedfurther herein.

Ignition timing control 22 may be any conventional type of devicesuitable for receiving an electrical timing control signal fromcontroller 12 and setting the timing of the ignition system of engine 24to a predetermined advance corresponding to the throttle position of theengine. Example ignition timing controls include actuators, relays andvalves suitable for controlling any or all of a mechanical, vacuum, orelectronic ignition control of engine 24. Ignition timing and advancecontrols are well-known in the art and thus will not be detailed furtherherein.

Engine 24 may be any type of engine now known or later developed thatgenerates motive power for a vehicle. Examples include, withoutlimitation, internal combustion (IC) engines, hybrid electric-IC enginesand electric motors.

Brake pedal state sensor 26 provides a status signal to controller 12 asto whether or not a brake pedal 32 of the vehicle is being actuated bythe driver. Brake pedal state sensor 26 may be any type of conventionalmechanical or electrical encoder, transducer or switch. Brake pedalstate sensor 26 may be powered by controller 12, or may be separatelypowered. The status signal provided to controller 12 by brake pedalstate sensor 26 may be any form of digital or analog electrical signalcompatible with the controller.

Accelerator pedal state sensor 28 provides a status signal to controller12 as to whether or not an accelerator pedal 34 of the vehicle is beingactuated by the driver. Accelerator pedal state sensor 28 may be anytype of conventional mechanical or electrical encoder, transducer orswitch. Accelerator pedal state sensor 28 may be powered by controller12, or may be separately powered. The status signal provided tocontroller 12 by accelerator pedal state sensor 28 may be any form ofdigital or analog electrical signal compatible with the controller.

Stability control selector 30 is a control, such as a switch actuable bythe driver of the vehicle to enable or disable a stability controlsystem of the vehicle. Stability control selector 30 is typicallylocated within convenient reach of the driver, on the dashboard or thegear selector lever. Alternatively, stability control selector 30 may bea conventional sensing device configured to monitor the stabilitycontrol system and provide to controller 12 a status signal indicatingwhether or not the stability control system is engaged. The stabilitycontrol system, when engaged by actuation of stability control selector30, automatically detects when the vehicle has deviated from thedriver's steered direction and compensates for oversteering,understeering and instability by selectively braking individual wheelsand/or reducing engine torque to bring the vehicle back on course. Suchsystems are well-known in the art and are commonly termed as “dynamicstability control,” “stability control program” and “electronicstability control,” among others.

With reference now to FIGS. 1, 2 and 3A-3D in combination, the operationof system 10 will now be described. The operation of system 10 begins atstep s100, controller 12 first checking brake pedal state sensor 26 atstep s102 to determine whether brake pedal 32 is being depressed (i.e.,actuated) by the driver of the vehicle. If brake pedal 32 is depressed(FIG. 3C), controller 12 checks accelerator pedal state sensor 28 atstep s104 to determine whether accelerator pedal 34 is also beingdepressed (i.e., actuated) by the driver. If accelerator pedal 34 isalso being depressed (FIG. 3A), controller 12 checks stability controlselector 30 at step s106 to determine whether the stability controlsystem is engaged.

If stability control selector 30 indicates that the stability controlsystem is not engaged, as at s108, drivetrain protection steps s110,s112 and s114 are executed. Controller 12 issues output commands tothrottle position actuator 20 at step s110 to set the actuator 20 (and,accordingly, engine 24) to a predetermined minimum throttle condition(FIG. 3A). Controller 12 also issues commands to ignition timing control22 to set the ignition advance to a predetermined minimum advancesetting corresponding to the predetermined minimum setting of throttleposition actuator 20. Controller 12 likewise issues commands totransmission gear selector 16 to place transmission 18 into apredetermined intermediate gear setting, such as second gear (FIG. 3D).In this configuration, even if the driver fully depresses acceleratorpedal 34 while actuating brake pedal 32 as indicated by FIGS. 3A and 3C,the amount of torque developed by engine 24 is at a predeterminedminimal value as indicated by the throttle position (FIG. 3A) andignition timing advance (FIG. 3B). These conditions continue while brakepedal 32 and accelerator pedal 34 are simultaneously depressed, therebyprotecting transmission 18 and engine 24 from high stress levels thatcould result in excess wear or damage thereto.

When brake pedal 34 is released at a subsequent time “T1” (FIG. 3C),controller 12 responds at step s115 by issuing commands to transmissiongear selector 16 to place transmission 16 into first gear (FIG. 3D).Furthermore, controller 12 issues normal-operation restoration commandsto throttle position actuator 20 and ignition timing control 22 to allowfor a ramp-up of engine 24 throttle (FIG. 3A) and ignition timingadvance (FIG. 3B), providing for a gradual increase in drivetrain 14output to amount that corresponds in a predetermined manner to theposition of accelerator pedal 34. Normal throttle, ignition timing andtransmission gear selection of drivetrain 14 are then maintained andsteps s100, s102, s104 and s115 are repeated while brake pedal 32 andaccelerator pedal 34 are not simultaneously actuated.

If both the brake and accelerator pedals 32, 34 are actuated at stepss102, s104 and if stability control selector 30 indicates that thestability control system is engaged, as at s116, drivetrain performancelimiting steps s118, s120 and s122 are executed as illustrated byreference to FIGS. 1 and 4A-4D. Controller 12 issues commands tothrottle position actuator 20 at step s118 to set actuator 20 (and,accordingly, engine 24) to a predetermined maximum throttle conditioncorresponding to the position of accelerator pedal 34. (FIG. 4A).Controller 12 also issues commands to ignition timing control 22 to setthe ignition advance to a predetermined maximum-limit advance settingcorresponding to a predetermined maximum setting of throttle positionactuator 20. Controller 12 likewise issues commands to transmission gearselector 16 to place transmission 18 into a predetermined low gearsetting, such as first gear (FIG. 4D). In this configuration thethrottle position and ignition timing of engine 24 are limited by system10 to the predetermined maximum-limit value, thereby providingdrivetrain 14 with a greater amount of torque for greater vehicleperformance than is available when stability control selector 30 is OFF.This may be desirable under certain adverse conditions, such as freeingthe vehicle when mired in snow or mud.

When brake pedal 34 is released (i.e., de-actuated) at a subsequent time“T2” (FIG. 4C), controller 12 responds at step s115 by issuingnormal-operation restoration commands to throttle position actuator 20and ignition timing control 22 to allow for an increase in engine 24throttle (FIG. 4A) and ignition timing advance (FIG. 4B), providing foran increase in drivetrain 14 output from the maximum-limit setting to anamount that corresponds in a predetermined manner to the position ofaccelerator pedal 34. Normal throttle, ignition timing and transmissiongear selection of drivetrain 14 are then maintained and steps s100,s102, s104 and s115 are repeated while brake pedal 32 and acceleratorpedal 34 are not simultaneously actuated.

It should be noted that the predetermined maximum-limit throttle andignition advance settings for the conditions of steps s118, s120, s122shown in FIGS. 4A and 4B are not necessarily equal to the maximumsettings that can be obtained when brake pedal 32 and accelerator pedal34 are not simultaneously depressed. For example, in some embodiments ofthe present invention the predetermined maximum-limit throttle settingand maximum-limit ignition advance timing may be significantly less thanthe maximum settings available for engine 24 under normal vehicleoperating conditions wherein brake pedal 32 and accelerator pedal 34 arenot simultaneously actuated. The predetermined maximum-limits for thethrottle setting and ignition advance timing are preferably establishedsuch that a greater amount of power is transmitted to the drive wheelsof the vehicle than the drivetrain protection mode steps s110, s112,s114 while still providing a measure of protection against damage orexcessive wearing of drivetrain 14.

The process of FIG. 2 ends at s124. The process may be repeated asdesired, as indicated by s126.

While this invention has been shown and described with respect to adetailed embodiment thereof, it will be understood by those skilled inthe art that changes in form and detail thereof may be made withoutdeparting from the scope of the claims of the invention.

1. A method for controlling operational characteristics of a drivetrainof a vehicle, comprising the steps of: providing the drivetrain with anengine, the engine being controlled by a positionable throttle and asettable ignition timing advance; providing the drivetrain with atransmission coupled to the engine, the transmission having a pluralityof gear settings; monitoring an actuation status of a positionable,operator-controlled brake pedal; monitoring an actuation status of apositionable, operator-controlled accelerator pedal; monitoring anengagement status of a stability control system; while both the brakepedal and the accelerator pedal are simultaneously actuated and thestability control system is not engaged, setting the throttle to apredetermined first position, setting the ignition timing to apredetermined advance corresponding to the first throttle position, andselecting a first gear setting of the transmission; and while both thebrake pedal and the accelerator pedal are simultaneously actuated andthe stability control system is engaged, setting the throttle to apredetermined second position, setting the ignition timing to apredetermined advance corresponding to the second throttle position, andselecting a second gear setting of the transmission.
 2. The method ofclaim 1, further comprising the step of selecting a predeterminedintermediate gear setting for the first gear setting of thetransmission.
 3. The method of claim 1, further comprising the step ofselecting a predetermined minimum throttle condition for the firstthrottle position.
 4. The method of claim 3, further comprising thesteps of: upon subsequent de-actuation of the brake pedal while theaccelerator pedal is actuated and the stability control system is notengaged, selecting a predetermined low gear setting for the first gearsetting of the transmission; and gradually increasing the output of thedrivetrain to a predetermined amount corresponding to the position ofthe accelerator pedal.
 5. The method of claim 1, further comprising thestep of selecting a predetermined low gear setting for the second gearsetting of the transmission.
 6. The method of claim 1, furthercomprising the step of selecting a predetermined maximum-limit throttlecondition for the second throttle position.
 7. The method of claim 6,further comprising the step of: upon subsequent de-actuation of thebrake pedal while the accelerator pedal is actuated and the stabilitycontrol system is engaged, increasing the output of the drivetrain to apredetermined amount corresponding to the position of the acceleratorpedal.
 8. The method of claim 1, further including the step of providingthe drivetrain with a throttle position actuator to control the throttleposition.
 9. The method of claim 1, further including the step ofproviding the drivetrain with an ignition timing control to control theignition timing advance setting.
 10. The method of claim 1, furtherincluding the step of providing the drivetrain with a transmission gearselector to control the gear setting of the transmission.
 11. The methodof claim 1, further including the steps of: providing a sensor tomonitor the actuation status of the brake pedal; providing a sensor tomonitor the actuation status of the accelerator; and monitoring theengagement status of the stability control system by one of monitoring acontrol selector switch or providing a status sensor.
 12. The method ofclaim 11, further comprising the step of selecting one of an encoder, aswitch and a transducer for each of the sensors.
 13. The method of claim1, further including the step of providing a stability control selectorswitch actuable by an operator of the vehicle to selectably engage thestability control system.
 14. A method for controlling operationalcharacteristics of a drivetrain of a vehicle, comprising the steps of:providing the drivetrain with an engine, the engine being controlled bya positionable throttle and a settable ignition timing advance;providing the drivetrain with a transmission coupled to the engine, thetransmission having a plurality of gear settings; monitoring anactuation status of a positionable, operator-controlled brake pedal;monitoring an actuation status of a positionable, operator-controlledaccelerator pedal; monitoring an engagement status of a stabilitycontrol system; while both the brake pedal and the accelerator pedal aresimultaneously actuated and the stability control system is not engaged,setting the throttle to a predetermined minimum throttle condition,setting the ignition timing to a predetermined advance corresponding tothe minimum throttle position, and selecting a predeterminedintermediate gear setting of the transmission; and while both the brakepedal and the accelerator pedal are simultaneously actuated and thestability control system is engaged, setting the throttle to apredetermined maximum-limit throttle condition, setting the ignitiontiming to a predetermined advance corresponding to the maximum-limitthrottle position, and selecting a predetermined low gear setting of thetransmission.
 15. The method of claim 14, further comprising the stepsof: upon subsequent de-actuation of the brake pedal while theaccelerator pedal is actuated and the stability control system is notengaged, selecting a predetermined low gear setting for the first gearsetting of the transmission; and gradually increasing the output of thedrivetrain to a predetermined amount corresponding to the position ofthe accelerator pedal.
 16. The method of claim 14, further comprisingthe step of: upon subsequent de-actuation of the brake pedal while theaccelerator pedal is actuated and the stability control system isengaged, increasing the output of the drivetrain to a predeterminedamount corresponding to the position of the accelerator pedal.
 17. Themethod of claim 14, further including the step of providing thedrivetrain with a throttle position actuator to control the throttleposition.
 18. The method of claim 14, further including the step ofproviding the drivetrain with an ignition timing control to control theignition timing advance setting.
 19. The method of claim 14, furtherincluding the step of providing the drivetrain with a transmission gearselector to control the gear setting of the transmission.
 20. The methodof claim 14, further including the step of providing a stability controlselector switch actuable by an operator of the vehicle to selectablyengage the stability control system.